In the aerobic biological treatment of wastewater and other liquids, it is common practice to provide an aeration system to oxygenate the liquid by dispersing pressurized air in a treatment vessel which contains the liquid. The aeration system is commonly comprised of an air distribution piping system including a main distribution header and submerged lateral pipes to receive air or another gas and apply it to diffusers which are mounted to the lateral pipes. The diffusers discharge the gas into the liquid in the form of bubbles. The highest efficiency aeration is achieved by using fine bubble diffusers such as porous membrane diffusers. However, less expensive coarse bubble diffusers are also used in some applications.
Three types of diffusers are commonly known in the wastewater treatment industry, including, (1) disc diffusers, such as those sold under the FlexAir® Disc name, (2) tubular diffusers, such as those sold under the FlexAir® Magnum™ name and (3) panel diffusers, such as those sold under the FlexAir® MiniPanel™ name. These diffusers systems are pipe-mounted systems, meaning that they include diffuser bodies mounted to the lateral pipes. The diffuser bodies are separate and apart from the lateral pipes. They are configured as individual bodies and then mounted to the lateral pipes.
Disc diffuser systems typically include a plurality of rigid circular diffuser bodies or holders mounted to the top of each lateral pipe. A perforated, flexible disc-shaped membrane is secured to the top of each diffuser body by a ring securing the peripheral edge of the membrane to the rim of the diffuser body. Each diffuser body includes a backer plate on which the membrane lies flat until gas is applied. When gas is applied to the diffuser body, the membrane is expanded and its perforations open to discharge gas in the form of fine bubbles. When the gas pressure is relieved, the membrane collapses on the backer plate and creates a seal that prevents liquid from leaking into the diffuser body.
Tubular diffuser systems typically include a plurality of rigid tubular diffuser bodies mounted to each lateral pipe in an orientation perpendicular to the lateral pipes. The tubular diffuser bodies may be screwed or otherwise mounted to extend horizontally perpendicular from the left and right sides of the lateral pipe. A perforated, flexible tubular membrane is positioned over each tubular diffuser body. Clamps may be used to secure the membrane to the diffuser body. When gas is applied to the diffuser body, the membrane is expanded and the perforations open to discharge gas in the form of fine bubbles. When the gas pressure is relieved, the membrane collapses on to the diffuser body and creates a seal that prevents liquid from leaking into the diffuser body. An example of a tubular diffuser of this type is found in U.S. Pat. No. 4,960,546.
Panel diffuser systems make use of a membrane bonded or otherwise secured to a frame which provides a plenum beneath the membrane. The membrane typically has perforations arranged in rows for discharging gas supplied to the plenum. Panel diffusers are functionally similar to disc diffusers and differ principally in that they have a rectangular horizontal projected geometry rather than a round disc shape as is the case with a disc diffuser.
Although the aforementioned diffuser systems function well for the most part, they are not wholly free of problems. They each involve a large number of parts thereby increasing their complexity, cost and maintenance requirements and decreasing their reliability.
Another shortcoming of currently known aeration systems involves the ability to remove and replace a single section or pipe located in the system. Aeration systems utilizing conventional mechanical couplers require an entire series of lateral pipes to be pushed apart in order to remove one pipe from within the series and then pushed back together once the pipe has been replaced. An individual lateral pipe cannot be removed and replaced without disturbing the adjacent pipes to which it is connected.
In practice, the most efficient aeration systems provide a relatively large area of perforated membrane and a relatively low amount of air flow per membrane. However, the aforementioned diffuser systems are often unable to achieve a high degree of efficiency primarily because, due to design and cost constraints, they are unable to achieve a relatively large area of perforated membrane as compared to the total surface area of the floor of the vessel in which they are installed.
An additional limitation for the size of the treatment vessel has been the length to which the diffuser system's lateral pipes could extend. As the temperature of the liquid in which the aeration system is located (or ambient temperature when the vessel is drained) varies, the system's lateral pipes expand and contract in length. The amount of linear expansion and contraction is described generally by the following:ΔL=α×L×ΔT                 ΔL=pipe's change in length        α=coefficient of linear expansion of pipe's material        L=pipe's length        ΔT=change in temperature        
As set forth above, the amount the pipe changes in length (ΔL) is directly proportional to the pipe's length (L). Thus, the longer the pipe, the more its length will change as a result of the varying of the temperature of the liquid in which it is submersed. Securing a lateral pipe fixedly at both ends or along its length results in force on the pipe and the brackets or mounts holding the pipe in place as the pipe expands and contracts. The pipe may bow and/or crack during the expansion and contraction. Additionally, the brackets or mounts holding the pipe may become bent or broken under the force. The maximum length of an unsupported span of pipe is limited by the pipe's deflection and, thus, couplers or supports are required in the use of normal sized aeration systems.
Thus, a need exists for a simplified aeration diffuser system having diffusers that are integral with the lateral pipes and not separate and apart therefrom. A need also exists for an aeration system wherein individual sections or pipes within the system can be removed and replaced without disturbing the adjacent sections or pipes. A need additionally exists for an aeration system capable of providing a large area of perforated membrane and a low amount of air flow per membrane. A need further exists for aeration system that can be of any desired length and not having a length dependent on mitigating the effects of the expansion and contraction of the lateral pipes therein. A need further exists for an aeration system wherein individual sections or pipes within the system can be removed and replaced without disturbing the adjacent sections or pipes.